Hearing tests are commonly given in two parts: an air-conduction test and a bone-conduction test. Results of these tests are displayed in the form of an audiogram. Audiograms are graphical representations of how well a person can perceive different sound frequencies. An audiologist gives an air-conduction test and/or a bone-conduction test and the results are displayed on an audiogram. During air-conduction testing, earphones are worn and the sound travels through the air into the ear canal to stimulate the eardrum and then the auditory nerve. The person taking the test is instructed to give some type of response such as raising a finger or hand, pressing a button, pointing to the ear where the sound was received, or saying “yes” to indicate that the sound was heard. The audiologist uses a calibrated machine called an audiometer to present tones at different frequencies (pitches) and at different intensity (loudness) levels. A tone at a particular frequency (something like a violin note) is presented to one ear, and its intensity is raised and lowered until the person no longer responds consistently. Then, another signal of a different frequency is presented to the same ear, and its intensity is varied until there is no consistent response. This procedure is commonly done for at least six frequencies. Then the other ear is tested in the same way.
During bone-conduction testing, a tone is introduced through a small vibrator placed on the temporal bone behind the ear (or on the forehead). This method by-passes blockage, such as wax or fluid, in the outer or middle ears and reaches the auditory nerve through vibration of skull bones. This testing operates in the same manner as the air-conduction testing and is done to measure functionality of the inner ear independent of the functionality of the outer and middle ears. The responses are also recorded on the audiogram. The audiologist then interprets the audiogram.
Audiograms take on many different forms, and audiologists often do not interpret a single audiogram in the same way. For a single ear, several variables (e.g., frequency selectivity of hearing loss, behavioral variability, and measurement error) can conspire to create an enormous number of possible audiograms. Applicant calculated the number of possible audiogram configurations for six air-conduction frequencies (octave frequencies 250-8000 Hz) and five bone conduction frequencies (octave frequencies 250-4000 Hz) with the following constraints:                a. Air-conduction thresholds can take any value between −10 and 110 dB HL (except at 250 Hz where the upper limit is 90 dB HL);        b. An air conduction threshold must be within 30 dB of the threshold at the next lowest frequency;        c. Bone-conduction thresholds can take any value between −10 and 60 dB HL except at 250 Hz where the upper limit is 40 dB HL;        d. A bone conduction threshold must be between −50 and 10 dB relative to the air conduction threshold at that frequency.With these constraints, there are more than 376 billion possible audiograms for a single ear. For an air-conduction only audiogram, there are 3.62 million possibilities.        
Since there are so many different audiogram possibilities, audiograms are very difficult to categorize. FIG. 1 illustrates an example of an audiogram that is difficult to categorize. In this audiogram, “X” indicates the left ear unmasked air-conduction, “Δ” indicates right ear masked air conduction, “[” indicates right ear masked bone conduction, and “]” indicates left ear masked bone conduction. Five expert audiologists each gave a different description of the right ear hearing loss configuration: flat, sloping, rising, trough, and other. All are reasonable descriptions. It is also difficult to describe the site of lesion for this audiogram. Most audiologists would characterize the hearing loss as sensorineural, but a mixed hearing loss cannot be completely ruled out.
FIG. 2 provides another example of a difficult to categorize audiogram. Three audiologists categorized the right ear configuration as flat and two categorized the configuration as sloping. Two audiologists considered the audiogram to be sloping because thresholds for high frequencies are at least 20 dB poorer than for low frequencies. Three audiologists were willing to overlook the thresholds at 6000 and 8000 Hz in favor of the more important 250-4000 Hz range and considered the audiogram to be flat. Either judgment is defensible.
As can be seen, audiologists often do not interpret a single audiogram in the same way. This makes it difficult to categorize audiograms by a concise and practical classification system. Audiogram classification systems have been attempted in the past. However, these systems have generally been unsuccessful. For example, some classification systems provide numerous categories, subcategories, labels, subscripts, and superscripts in order to accommodate for the numerous interpretations. However, a classification system having too many categories is not practical for clinical application. Other classification systems do not account for disagreement among audiologists. For example, some classification systems provide general rules for placing audiograms in categories but do not deal with the practical issue of assigning a category when audiologists disagree or when there are local irregularities that audiologists learn to ignore. Also, local irregularities sometimes occur on an audiogram, and many audiologists ignore these when classifying audiograms. Known classification systems do not take into account local irregularities.
It would be desirable to provide an audiogram classification system that has clinical applications. It would be particularly desirable to provide a concise and practical audiogram classification system that does not have an overwhelming number of categories. It would also be desirable to provide a classification system that maximizes the likelihood that the selected classification of the audiogram agrees with audiologists. It would also be desirable to provide a classification system that also accounts for local irregularities that audiologists often ignore.
When interpreting audiograms, audiologists often use personal and subjective rules. As a result, it is difficult to analyze and compare subjectively categorized audiograms. Thus, it would be desirable to provide a standardized classification system with a standardized, non-subjective set of rules, so that audiograms categorized can be accurately analyzed and compared in order to study hearing loss trends, to correlate hearing loss types with ear disease, and so on.
Audiograms are also classified by audiologists manually, rather than by an automated program. It would be desirable to provide an automated classification system, since such a system would be easier to administer and would provide more consistent results.
In clinical settings, once an audiogram has been generated, an audiologist typically prescribes a treatment. Often times, the recommended treatment is a hearing aid. A variety of hearing aid types are available and audiologists commonly select a type that works best with a given hearing loss category. It would be desirable to provide a classification system that correlates hearing loss categories with hearing aid types. In some cases, it would be desirable to provide an automated classification system that automatically produces a hearing aid prescription that is correlated to a particular audiogram classification.